Method for producing non-metallic magnetic materials



United States Patent 3,129,184 METHOD'FOR-PRODUCIN G NON-METALLICMAGNETIQMATERIALS Christopher Nigel .KenneyandRaymond-Speneer-Thornhill, Northwich, England, assignors to ImperialChemical IndustriesLimited; London, England, a. corporation GreatBritain; N0 Drawing. Filed May 25, 1961, Ser. Nix-112,535 Claimspriority, application Great Britain- May 7 3'1, 1960 4-.Claims. (Cl..252-.62.5).

This invention, relatesxto'aniimproved process for the manufacture ofnon-metallic magnetic materials known collectively as ferrites;and;having thegeneral empirical formula wherein M, M', and M''areidivalentrnetals, such for example as magnesium, zinc, barium,manganese,,nickel, cobalt, and x, yand z-have any,value-including-zerobut are such that (x-l-y-l-rz); is, between 0 and 2.

In British Patent-No.1793, 8.70 we-,-have disclosed and claimed ahydrothermal .processfor making ferrites characterised in that thecomponent oxides, or derivatives thereof 'such as; carbonates-andhydroxides, are caused to. react together by heating under: pressure;with water or steam at temperatures above 100C.

In the; examples illustrating the invention of British Patent No.793,870 the oxide of ironused 1is-ferric oxide F620;}. We have: now-folndthatferrites: having much improved magnetic:properties.comparediwiththose made with ferric oxide are obtained :.by :u.sing in.the;.said;hydrothermal process a particular. oxide of iron namely thehydroxy-oxide known as goeth'ite and defined as According to, thepresent; invention-therefore; a process for making compounds ofjtheigeneral'formula wherein M, M, M represent divalent metals, and10,is oxygen, and x, y and 1 may have any-valueincludingzero.bnt. are suchthatitheir' sumlies betweenO and-2,

by mixing. the component oxides or. derivatives-thereof suchascarbonates .and hydroxides, and-heating the mix-; ture undersuperatmospheric pressure with water: Qr;steam, at temperatures above100 C. is characterised in that the oxide Ofjll'OIl isth'ehydroxy,-oxide defined;as a-Ee.0(OH).

Iron forms. three hydroxy-oxidesnamely,- a-FeO(OI-I) known as geothite,,B-FeO(OH) known as lepidOCIOtJite, and 6-FeO( OH-) They-lose-water-atrelatively -low temperatures within the range i100'2510"C. through the transformation of a-FeO(OI:I,-) toFe Q is notcompleteuntil somewhat higher temperatures. The fl-hydroxyoxide will also yieldmagnetic ferrites by the said hydrothermal process but theu-hydroxy-oxide not only gives rise to ferrites having superior magneticproperties which make them commercially valuable, but does so in muchhigher yields. It is not known why a-F60(OH) behaves in this way; it ispossible that its superior ability to absorb other ions has a bearing onthe matter. Thus, if a-F60(OH) is stirred in a solution of bariumhydroxide it removes nearly twice as much barium from solution as Fe Odoes under similar conditions. Another possibility is that compared withFe O the hydroxy-oxide has a less rigid internal structure, thus morereadily allowing penetration of its lattice by other ionic species.

Magnetic ferrites, as is known, may have permanent or temporary magneticproperties and are described as 'hard and soft ferrites respectively.Both kinds can be made in good yield by using oc-F60(OH) in thehydrothermal process. Barium fel'rite BaO.6Fe O* is an example of thehard ferrites so made, and nickel/zinc, nickel/ zinc/manganese and-fmagnesium/manganese ferrites. of thesoft type.,

One way of carrying out the hydrothermal'process is to mix the requireddry oxides, hydroxides or carbonates, and to place thermixture in anautoclave. and then to add water and thoroughly mix to a thin slurry,after which the autoclave is closed and the temperatureraised to a valuewithinthe'range 400? C ,prefer ably 30,0,-. 350,, and'keptther forseveralhours, for examp1e4- to 20., In another way solublesaltsofthemetals, .othcrthaniron, whose oxides are toreacttoform'-the-ferrite may be added {to the autoclave together withthe a-FeO(OH) and slurried with a dilutesolution of caustic soda wherebythe corresponding hydroxides are formed, after which the autoclave .isclosed and heated asbefore.

When the reaction is overthe autoclave iscooled and opened and, ifdesired, any .unreacted oxidesmay. be separated from the ferriteeitherby dissolving themin a dilute mineral acid or magnetically. Theferrite is then ready. for knworrshaping, firing andmagnetisingoperaitons as desired.

Theflinvention is illustratedby. the following examples Nos: 1,-4rofwhich show. with respect to the hard ferrite, barium. ferrite, the.advantage to be gained by. using ot-EeO(OH) in place of. lie- 05; Nos. 5and 6.show-a similar adv-antageinrespect of asoft ferrite,nickelferrite. The remaining examplesillustrate the preparation ofdifferent ferrites.

Example 1 Ferric oxide, (325" g) and hydrated bariumhydroxide Ba (OH.).8H O' (113g);weremixedendslurried in 30, mls. water, and thenheatedinan unstirrred autoclave under autogenous pressure for 4,hours.at' 350?C. The resultingbarium fe'rritepowder was then mixedw-ith a 1% solutionof glycerine in, methanol 7 to serve as a binder, pelleted in a ,mould,under a; pressure of 1000, kgjsq. inch, andfiredat 1250? C. foronehour. The pelletv after magnetisation to saturation hadaremanencevalue B; of'880 gauss.

Example 2 The preparation described in Example lwas repeated except thatocF60(-OH-) (30.6- g.-)- was used'instead of ferric oxide. Theremaneneevalue was .1550 .gauss.

Example. 3

' The preparation described in Example 1 was repeated with 40 g. offerric oxide, 147 g. of hydrated barium hydroxide-,and 3olmls. Water,and;a,1onger:heating. time in the autoclave namely: 10 hours. The.remanence value was .0.Qgat1ss;v

Example 4 The preparation described in Example 3 was repeated exceptthat oz-F60(OH) (30.6 g.) was used instead of ferric oxide. Theremanence value was 1820 gauss.

Example 5 Example 6 The preparation described in Example 5 was repeatedwith 35.6 g. of a-FeO(OH) replacing the ferric oxide. The product showeda spinel structure by X-ray crystallographic analysis and had aninduction value at 10 oersteds B of 1800 gauss and a coercivity H of 0.3oersted.

3 Examples 7-12 These examples show for a given mixture of a-FeO(OH)(30.6 g.) and hydrated barium hydroxide (10.4 g.) the effects ofdifferent proportions of water and of reaction time and temperature. Allthe barium ferrite products after shaping in the moulds were fired at1:220- 1250 C. for one hour.

a F6O(OH) (35.9 g.), MnCO (7.6 g.), ZnO (6.4 g.) and N (0.23 g.) weredried and well mixed, placed in an autoclave and slurried with 30 mls.water and heated under autogenous pressure for 16 hours at 350 C. 20grams of the dry manganese/zinc/nickel ferrite product was mixed with 3mls. polyvinyl alcohol in water as binder and shaped in a ring mouldunder 4000 lbs./ sq. inch pressure. The ring was dried at 105 C. andthen raised to 1310 C. over 4 hours in a Weakly oxidising atmosphere,and kept at this temperature for one hour and then cooled over 8 hours.Its induction value B, at 10 oersteds was 2370 gauss and its coercivityH 0.25 oersted.

Examples 14-16 In these examples the hydroxides of the metals, except ofiron, were made in situ in the autoclave by the action of caustic sodaon their salts. The reaction mixture consisted of a-FCO(OH) (20 g.),Zn(-NO .6H O (13 g.), MnCl .4H O (9.5 g.) and NiSO .7H O (0.95 g.), andthese in terms of oxides were in the same molecular ratios as in Example13. The dry salts were mixed and placed in the autoclave, slurried with50 mls. water and then 12 g. NaOH dissolved in 50 mls. water was added,and the mixtures heated as before but under diiferent pressures and theproducts shaped and fired as in Example 13.

The reaction mixture consisted of a-F60(OH) (27.7 g) and MnCO (22.1 g.)and 30 mls. water and it was heated at 350 C. for 16 hours underautogenous pressure. The

manganese ferrite after shaping and firing as in Example 13 had a B,value at 10 oersteds of 2360 gauss and a coercivity H of 0.25 oersted.

Example 18 The reaction mixture consisted of a-FeO(OH) (42 g.) NiO (6.1g.) and MnO (12.4 g.) and 80 mls. water, and it was heated at 350 C. for24 hours under autogenous pressure. After shaping and firing as inExample 13 the nickel/zinc ferrite had a B value at 10 oersteds of 1520gauss and a coercivity H of 0.25 oersted.

What we claim is:

1. A process for the manufacture of a non-metallic magnetic compoundhaving the general formula wherein M, M, and M" represent divalentmetals selected from the group consisting of magnesium, zinc, barium,manganese, nickel, and cobalt, O is oxygen, and x, y and z are numberssuch that the ratio of divalent metal to said Fe O is at least in therange of 1:6 to 1:1 which comprises mixing an oxygen containingderivative of at least one of said divalent metals selected from thegroup consisting of the oxide, carbonate, and hydroxide derivativesthereof, with an iron oxide defined as and heating the resulting mixturefor from about 4 to about 20 hours at a pressure within the range of 10to 100 atmospheres and a temperature within the range of 100 to 400 C.with a member of the group consisting of water and steam.

2. A process for making barium ferrite BaO.6Fe O as defined in claim 1in which a thin aqueous slurry of a mixture of the hydroxy-oxide ofiron, defined as and barium hydroxide is heated at 300350 C. underautogenous pressure for from 4 to 10 hours.

3. A process for making nickel/zinc/manganese ferrites as defined inclaim 1 in which a thin aqueous slurry of a mixture of magnanesecarbonate 'MnCO zinc oxide ZnO, nickelous oxide NiO, and thehydroxy-oxide of iron a-FeO(OH) is heated at 300-350 C. under autogenouspressure for from 4 to 20 hours.

4. A process as defined in claim 1 in which the hydroxides of the metalsother than iron are made in situ in the hydrothermal reaction system bythe action of caustic soda on their salts.

References Cited in the file of this patent UNITED STATES PATENTS2,978,414 Harz et al Apr. 4, 1961 FOREIGN PATENTS 793,870 Great BritainApr. 23, 1958

1. A PROCESS FOR THE MANUFACTURE OF A NON-METALLIC MAGNETIC COMPOUNDHAVING THE GENERAL FORMULA